Medium [CVE-2026-64239] delete tried region in regions_rmdirs
This medium-severity Red Hat Linux advisory covers CVE-2026-64239 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat package: kernel-rt.
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Summary
In the Linux kernel, the following vulnerability has been resolved: mm/damon/sysfs-schemes: delete tried region in regions_rmdirs() DAMON sysfs maintains the DAMOS tried region directory objects via a linked list.
When the user requests refresh of the directories, DAMON sysfs removes all the region directories first, and then generate updated regions directory on the empty space. The removal function (damon_sysfs_scheme_regions_rm_dirs()) only puts the kobj objects.
Deletion of the container region object from the linked list is done inside the kobj release callback function. If somehow the callback invocation is delayed, the list will contain regions list that gonna be freed.
If the updated region directories creation is started in this situation, the list can be corrupted and use-after-free can happen. Because the kobj objects are managed by only DAMON sysfs, the issue cannot happen in normal situation.
But, such delays can be made on kernels that built with CONFIG_DEBUG_KOBJECT_RELEASE.
On the kernel, the issue can indeed be reproduced like below. # damo start --damos_action stat # cd /sys/kernel/mm/damon/admin/kdamonds/0/ # for i in {1..10}; do echo update_schemes_tried_regions > state; done # dmesg | grep underflow [ 89.296152] refcount_t: underflow; use-after-free.
Fix the issue by removing the region object from the list when decrementing the reference count.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · medium-confidence parse· fetched 12 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 12 days ago·verify at source
Mitigation
The source record does not include mitigation steps. That is not a statement that no fix exists — read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 12 days ago·verify at source
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